1. Field of the Invention
The present invention relates to a video signal digital recording and reproducing apparatus for recording or reproducing a digital video signal on a recording medium using a bit rate reduction method.
2. Description of the Prior Art
As a conventional video signal digital recording and reproducing apparatus, there is for example a rotary head type digital VCR for directly recording pixel data without providing any bit rate reduction.
FIG. 8 shows a block diagram of a conventional video signal digital recording and reproducing apparatus. In FIG. 8, element is a first error correcting code encoder; element 2 is a shuffling memory; element 3 is a second error correcting code encoder; element 4 is a magnetic tape, 5 is a second error corrector, 6 is a deshuffling memory, and element 7 is a first error corrector. A digital video signal is inputted to the first error correcting code encoder 1, and, with addition of an error correction code, written in the shuffling memory 2. In the reading out of the shuffling memory 2, the digital video signals are read out at random on a pixel by pixel basis with a change of the order of the digital video signals. The read out signals are once again provided with error correction codes based on the sequence of the rearranged pixel data by the second error correcting code encoder 3 and recorded via a magnetic head on the magnetic tape 4. In reproducing, the signals reproduced from tape 4 via a magnetic head are subjected to a correction of errors by the second error corrector 5 and written in the deshuffling memory 6. In the deshuffling memory 6, rearrangement of pixel data is carried out in reverse order to the rearrangement of pixel data in the shuffling memory 2 in recording to reinstate the sequence of the pixels to their original state. Thereafter, the reproduced signal is again subjected to error correction with the first error corrector 7 and outputted as a digital video signal. In this case, the reason for rearranging the sequence of the pixels is not only to obtain the efficiency of error correction but also to make the image in a high speed reproduction mode easily observed with a digital VCR. In the high speed reproduction mode of a digital VCR, the head on the rotary drum traverses obliquely to the tracks recorded on the tape, as shown in FIG. 9. Accordingly, the detectable signals are on the skipped places against the recorded patterns. In a digital VCR, a high speed reproduced picture is to be constituted by using only the pixel data which has been detected. In such a case, there is an effect that, when shuffling is in effect, the detected pixels are scattered over the whole screen, and no unnatural discontinued section appears on the screen.
However, when a digital VCR using bit rate reduction is considered, compression of information is carried out by a method such that, as shown in FIG. 10, the pixels on the screen are sectioned in rectangular shapes, each rectangular unit is subjected to orthogonal transformation and then to variable length coding, and information of a certain number of rectangular units are gathered to form a block of fixed length. However, when these rectangular units are shuffled to carry out digital recording, different from the shuffling on a pixel by pixel basis, the screen images in a high speed reproduction mode become mosaic shaped to show a state which is very difficult to observe. On the contrary, when the video information in rectangular units is recorded in the original sequence without shuffling, the rectangular units in each fixed length block lie on the positions adjacent to one another on the screen, by which a deviation of in the amount of information occurs so as to cause a problem in that the effect of high efficiency coding is diminished.
In view of the abovementioned points, the present invention has its object to provide a video signal digital recording and reproducing apparatus which satisfies both the easiness to observe video images in a high speed reproduction mode and the efficiency of bit rate reduction.